This invention relates generally to the field of integrated circuit fabrication, and more particularly to a method for moat nitride pull back for shallow trench isolation.
Modern electronic equipment such as televisions, telephones, radios and computers are generally constructed of solid state devices. Solid state devices are preferred in electronic equipment because they are extremely small and relatively inexpensive. Additionally, solid state devices are very reliable because they have no moving parts, but are based on the movement of charge carriers.
Solid state devices may be transistors, capacitors, resistors, and other semiconductor devices. Typically, such devices are formed in and on a substrate and are interconnected to form an integrated circuit. However, semiconductor components must be properly isolated from one another to function properly. For example, the state and conductance of individual transistors can only be controlled if proper isolation exists among the transistors. If not, leakage currents may occur, causing power dissipation, noise-margin degradation, and voltage shift on dynamic nodes. Additionally, cross talk among transistors can destroy the logic state of a gate.
One way to address these problems are through the formation of shallow trench isolation (STI) structures. STI structures have been used for sub 0.5 micron applications. Typically, a narrow trench is formed in a substrate, and the trench filled with an insulating material (xe2x80x9cSTI fillxe2x80x9d). One problem that has been observed is a tendency of sharp corners or divots to form in the trench isolation material during subsequent etching, deglazing, or other processes subsequent to STI fill.
One method that has been developed for addressing this problem is moat nitride pull back. Moat nitride pull back involves lateral recessing the edge of the moat nitride layer at an isolation trench with a phosphoric acid etch or another suitable process before filling of the trench with isolation material, such that lateral recesses or cavities at the upper corners of the isolation trench may be formed. Isolation material may fill these lateral recesses as well as the trench, thus allowing the deposited isolation material to extend upward and outward from the isolation trench. By allowing the isolation material to extend upward and outward from the trench, the tendency of sharp corners or oxide divots to form in the trench isolation material during subsequent etching, deglazing, or other processes may be reduced.
The present invention provides a method for moat nitride pull back for shallow trench isolation that substantially eliminates or reduces disadvantages and problems associated with prior systems and methods.
In accordance with one embodiment of the present invention, a method of fabricating a shallow trench isolation structure includes forming outwardly of a semiconductor layer a first oxide layer. A nitride layer is formed outwardly of the first oxide layer. A second oxide layer is formed outwardly of the nitride layer. A trench is formed through the first oxide layer, the nitride layer, and the second oxide layer and into the semiconductor layer. With the second oxide layer protecting an upper surface of the nitride layer, the nitride layer is etched to form a lateral recessed side boundary of the trench at the nitride layer. The shallow trench isolation layer is formed in the trench.
Technical advantages of the present invention include an improved method of moat nitride pull back for STI. The presence of the oxide layer during moat pull back may allow for more control over the moat nitride pull back process.
Another technical advantage of the present invention includes the reduction in the number of deglazing steps required for transistor manufacture. In accordance with various embodiments of the present invention, the formation of oxy-nitride on the nitride layer is reduced or eliminated, thus reducing or eliminating the need for a separate deglaze step to remove oxy-nitride from the nitride layer.
Another technical advantage of the present invention includes a reduction in thickness variation in the nitride layer, resulting in better control over, and less potential damage from, chemical-mechanical polishing. In traditional methods, etching of the nitride for moat nitride pull back will remove part of the top of the nitride layer, exacerbating thickness variations in the nitride. In accordance the present invention, the oxide layer may protect the surface of the nitride during nitride pull back, thus reducing or eliminating nitride thickness variations resulting from the pull back step.
Certain embodiments may possess none, one, some, or all of these technical features and advantages and/or additional technical features and advantages. Other technical advantages will be readily apparent to one skilled in the art from the following figures, description, and claims.